A trader inadvertently booked a trade with incorrect information.

When a trader inadvertently books a trade with incorrect information and a subsequent market move results in a gain for the bank, the event should be included in the operational loss event data program because:

Indication of Control Failure (II):The gain indicates that a control failed or a process is flawed. Even if the outcome was a gain, the underlying issue was a mistake, pointing to a weakness in the bank's operational controls that needs to be addressed.

Recording the Event as a Loss (III):Although the event resulted in a gain, it should be included in the operational loss event data program and recorded as a loss. The principle behind this is to ensure that all operational risk events are tracked, irrespective of their financial outcome, to provide a complete picture of operational risk exposures and to improve risk management practices.

Including such events helps in identifying and correcting process flaws to prevent future incidents that could result in actual losses.

References

How Finance Works.pdf, Index section​